Brewer's: Filioque Controversy
(The) long disturbed the Eastern and Western Churches. The point was this: Did the Holy Ghost proceed from the Father and the Son (Filio-que), or from the Father only? The Western Church maintained the former, and the Eastern Church the latter dogma. The filio-que was added in the Council of Toledo 589. Amongst others, Pope Leo III. was averse to the change. (Nicene Creed.)
The gist of the argument is this: If the Son is one with the Father, whatever proceeds from the Father must proceed from the Son also. This is technically called ?The Procession of the Holy Ghost.?